Promoted platinum-iridium-containing reforming catalysts

ABSTRACT

Process and composition for improving the octane quality of naphthas. An iridium-containing catalyst, particularly a catalyst of an admixture of platinum, iridium, and either iron or bismuth, or both, composited with a porous, inorganic oxide base, inclusive of halogen, is found especially useful in reforming particularly in redispersing agglomerated iridium in reactivation of the catalyst.

This is a division of application Ser. No. 388,907, filed Aug. 16, 1973,now U.S. Pat. No. 3,867,280.

Catalytic reforming, or hydroforming, is a process well known to thepetroleum refining industry and has been used for improving the octanequality of naphthas and straight run gasolines for decades. In a typicalprocess, a series of reactors are provided with fixed beds of catalysts,and each reactor is preceded by a reheat furnace. A naphtha feed, withhydrogen, is co-currently passed sequentially through a reheat furnaceand then, downflow, to the preceding reactor of the series. The vaporeffluent from the last reactor of the series is a gas rich in hydrogen,which usually contains small amounts of normally gaseous hydrocarbons,and it is separated from the C₅ ⁻ liquid product and recycled to theprocess to inhibit coke formation on the catalyst, though overall thereis net hydrogen production.

Reforming catalysts are recognized as dual-functional, the catalystcomposite incuding a component comprising a metal, or metals, or acompound or compounds thereof, usually as oxides or sulfides, providinga hydrogenation-dehydrogenation function and a mildly acidic componentproviding an isomerization function. The principle reactions produced bydual functional reforming catalysts: (1) the dehydrogenation ofnaphthenes to produce the corresponding aromatic hydrocarbons, e.g.,methylcyclohexane is dehydrogenated to form toluene, (2) isomerizationof n-paraffins to form branched-chained paraffins and isomerization ofring compounds, e.g., the isomerization of ethylcyclopentane to formmethylcyclohexane, and dehydrogenation of the latter to form toluene,(3) dehydrocyclization of paraffins to form aromatics, e.g., thedehydrocyclization of n-heptane to form toluene, and (4) hydrocrackingof high molecular weight feed constituents to form lower molecularweight, or lower boiling constituents, e.g., the cracking of n-decane,to produce C₃ and C₇ hydrocarbons. The net effect of such reactions mustbe to increase the concentration of aromatics, with consequent octaneimprovement of naphthas boiling within the gasoline range.

Group VIII noble metals, i.e., platinum group metals (ruthenium, osmium,rhodium, iridium, palladium, and platinum), despite their expense, havelong since been recognized as having a combination of properties whichmake them particularly suitable as hydrogenation-dehydrogenationcomponents for reforming operations, and catalysts, utilizing platinum,have become widely used in commercial operations. Conventional reformingcatalysts have thus long employed platinum composited with an inorganicoxide base, particularly alumina. More recently, due to environmentalconsiderations which necessitate removal of lead from gasoline, othermetals such as rhenium, germanium, tungsten, tin, lead, and Group IIIrare earth metals have been added to platinum as promoters to enhanceone or more of certain of the characteristics which a good reformingcatalyst must possess--viz., activity, selectivity, activitymaintenance, and yield stability. Minor proportions of a halogen, e.g.,chlorine, are generally added to supply the acid function required ofsuch catalysts.

Iridium-containing catalysts, or catalysts comprising, e.g., compositesof platinum and iridium with an inorganic oxide base, particularlyalumina, were reported many years ago and are described in, e.g., U.S.Pat. No. 2,848,377. While such catalysts are significantly more activein the production of C₅ ⁻ gasoline during reforming than a catalystcomprising platinum without iridium, the commercial application of suchcatalyst has lagged, and only recently has such catalyst been seriouslyconsidered for commercial use. Though the initial activity of thesecatalysts is generally high, and activity maintenance is excellent, aprogressive and serious decline in activity does occur. There is atendency of the iridium to form larger aggregates, or agglomerates,generally in admixture with iridium oxide. As the size of theagglomerates increases, there results a progressive decline in catalystactivity.

X-ray diffraction patterns taken, e.g., on fresh, or carefullyregenerated, platinum-iridium catalysts thus fails to show anysignificant lines corresponding to platinum, or iridium, thus indicatingthat platinum and iridium are present in very finely dispersed atomicforms. X-ray diffraction patterns taken on the same catalyst used inreforming, from which the coke has been burned, shows the presence ofplatinum and iridium, as agglomerates or relatively large or massivecrystals with crystal diameters in excess of about 50A (Angstrom units)and even 150A, and greater. The crystallite size of the platinum issharply contrasted with the state of dispersion of the platinum on freshcatalysts which is shown by carbon monoxide chemisorption techniques torange in average size to a maximum of about 11 or 12A. (See J. ofCatalysis, 8 348,1967 by D. J. C. Yates and J. H. Sinfelt.) Iridiummetal not only exhibits similar behavior but, additionally, especiallyin the presence of oxygen at high temperature, possesses an acutetendency to agglomerate into large crystallites which contain iridiumoxide in admixture with the agglomerated metal. The activity of suchcatalysts is substantially lowered as a result of the loss of metaldispersion on the catalytic surface.

Satisfactory techniques have only recently been discovered forredispersing iridium and iridium oxide containing agglomerates. Inaccordance with these procedures, it has been found that theagglomerates of iridium-containing catalysts can be redispersed, and thedeactivated catalyst thereby reactivated, by sequential (a)prereduction, preferably with hydrogen, (b) with subsequent contact ofthe reduced catalyst with halogen, or halogen-containing gaseousmixtures, e.g., chlorine or chlorine-containing gaseous mixtures, whichmay or may not contain oxygen. Of the techniques described, multiplecycle treatments of (a) prereduction, and (b) halogen contacts are morepreferred in reactivation of the iridium-containing deactivatedcatalysts. These techniques have proven effective in redispersingiridium agglomerates, particularly multiple cycle treatments which can,in varying degrees of effectiveness, completely redisperse the iridiumagglomerates.

The present invention embodies a process for improving the octanequality of a naphtha by contacting said naphtha, at reformingconditions, with a highly active catalyst composite, and the catalystcomposite itself which includes a porous inorganic oxide support andcatalytically active amounts of iridium, particularly platinum, andiridium, promoted with iron or bismuth, or both. Suitably, thecomposition is comprised of from about 0.05 to about 3 weight percent,preferably from about 0.1 to about 0.6 weight percent, platinum, fromabout 0.05 to about 3 weight percent, preferably from about 0.15 toabout 0.3 weight percent iridium, and from about 0.05 to about 5 weightpercent, preferably from about 0.5 to about 2 weight percent, of iron orbismuth. Suitably also, the composite includes from about 0.1 to about 2weight percent, and preferably from about 0.6 to about 1.5 weightpercent, of a halogen, e.g., chlorine, bromine, fluorine, and the like,of which chlorine is preferred. These metalhydrogenation-dehydrogenation components are generally present in thecomposite as a compound, or compounds, of the metal, or metals,generally as an oxide, halide or sulfide, or mixtures thereof. Thecomposition can also include additional metals, or compounds of metals,as hydrogenation-dehydrogenation components, e.g., palladium, rhodium,osmium and the like, provided they are not contained in concentrationsufficient to substantially decrease the normal catalytic effect of theadmixture of platinum, iridium and iron or bismuth.

The reason for the effectiveness of iron and bismuth in "promoting" suchcatalysts is not completely understood, but halide-containingplatinum-iridium catalysts promoted in such manner possess increasedresistance to agglomeration and, if agglomerated, the agglomerates aremore readily redispersed by conventional redispersion techniques. It isbelieved that iron and bismuth, at redispersion conditions, combine withthe halide, e.g., chlorine, and provide a chloronium ion which reactswith iridium oxide, IrO₂, to form IrO₂ Cl, which is more readilyredispersed than IrO₂ which is especially inert to redispersion. Anothertheory, however, is that the iron acts as a "getter" and suppresses theformation ab initio of iridium oxide agglomerates. Iron, in any event,whether it acts as a promoter or inhibitor, is particularly suitable,and is preferred because not only does it aid in redispersion but alsothe activity of the iron-containing platinum-iridium catalyst isincreased as contrasted with the non-iron containing platinum-iridiumcatalyst and, in addition C₅ ⁻ liquid yield, activity maintenance andoctane yield relationships are not significantly adversely affected, ifat all.

In the practice of this invention, suitably, the metalhydrogenation-dehydrogenation components are composited with mildly ormoderately acidic refractory inorganic oxides which are employed assupports, e.g., silica, silica-alumina, magnesia, thoria, boria,titania, zirconia, various spinels and the like, including in particularalumina which is preferred. High surface area catalysts, or catalystshaving surface areas ranging upwardly from about 100 square meters pergram are preferred. In particular, catalysts having surface areasranging from about 160 to about 250 square meters per gram prove quitesatisfactory.

In formation of the more active catalysts, porous refractory inorganicoxides of desired particle size distribution, in dry state, can becontacted, admixed, or otherwise incorporated with a metal-containingsolution, or solutions, and thereby impregnated. The refractoryinorganic oxide can thus be pilled, pelleted, beaded, or extruded, aloneor in admixture with other materials, and dried and crushed to formparticles of desired size ranging, e.g., from about 0.02 to about 0.4inches, and preferably from about 0.05 to about 0.2, average diameter.The material can then be treated by contact with a solution containingdesired amounts of platinum, iridium and iron or bismuth, or treatedsequentially by contact with a solution containing one metal and thenanother in the desired amounts. On the other hand, larger particles canbe so treated and then crushed to the desired size. The particulatemass, in either instance, can be dried, calcined, and contacted withhydrogen, in situ or ex situ, to reduce the salt. Suitably, also, thecatalyst composite can be formed by adding together suitable reagentssuch as salts of platinum, iridium, iron or bismuth, and ammoniumhydroxide or ammonium carbonate, and a salt of alumina such as aluminumchloride or aluminum sulfate to form aluminum hydroxide. The aluminumhydroxide containing the salts of platinum, iridium, and iron or bismuthcan then be heated, dried, and simultaneously converted to alumina,impregnated with platinum, iridium, and iron or bismuth salts. Thematerial can then be calcined and then hydrogen-treated, in situ or exsitu, to reduce the salts and complete the formation of the catalystcomposite.

Essentially any hydrocarbon fraction containing paraffins, naphthenes,and the like, can be converted by means of the catalysts of thisinvention. A suitable feed, e.g., either virgin or cracked,Fischer-Tropsch or mixtures thereof, is contacted at reformingconditions in the presence of hydrogen (once-through, or recycle) with acatalyst composite including a support which contains catalyticallyactive amounts of the metals. Typical feed stream hydrocarbon moleculesare those containing from about 5 to about 12 carbon atoms, or morepreferably from about 7 to about 9 carbon atoms. Naphthas, or petroleumfractions boiling within the range of from about 80°F. to about 450°F.,and preferably from about 125°F. to about 375°F., contain hydrocarbonsor carbon numbers within these ranges. Typical fractions thus usuallycontain from about 20 to about 80 vol. % of paraffins, both normal andbranched, which fall in the range of about C₅ to C₁₂, from about 20 toabout 80 vol. % of naphthenes boiling within the range of about C₆ toC₁₂, and about 5 through 20 vol. % of the desirable aromatics boilingwithin the range of about C₆ to C₁₂.

Total cycle time is constituted of an on-oil portion and a regenerationportion of a cycle of operation. Regeneration and reactivation of thecatalyst to maintain high catalytic activity is essential in thepractice of this invention. In accordance with the present invention,therefore, deactivated catalyst is periodically reactivated. Forexample, in a reactor system wherein several reactors are in series, asingle reactor is swung out of the series periodically, is regeneratedand reactivated, and then put back in series, albeit all reactors of theseries are not swung in and out of series with the same frequency. Thus,the catalyst in the end or tail reactors will generally be regeneratedmore frequently than catalyst in the front reactor, or reactors. Forexample, the front reactors may operate for several hundred hours beforeregeneration, whereas the tail reactor might only operate 20 to 100hours before regeneration.

The exact time that a specific reactor can be used between regenerationsis a function of many variables; for example, the particularconcentrations of the hydrogenation-dehydrogenation component andhalogen in the catalyst, the pressure, liquid hourly space velocity,temperature of the reforming process, and the like. It is generallypreferred for reasons of economy to operate the reactors for as long aperiod as possible between regenerations without sacrificing substantialvaluable C₅ ⁻ liquid yield. Regeneration time is generally short incomparison to the overall reforming time.

The catalyst is regenerated by heating it in the presence of anoxygen-containing gas to burn coke off the catalyst. It is desirable topurge the reactor of hydrogen and naphtha before beginning theregeneration step. This can be accomplished by purging the reactor withan inert gas, e.g., flue gas. Oxygen is then generally added to theinert gas in limited amount. The oxygen in the regeneration gas shouldgenerally not exceed about 1 volume percent. Excess oxygen is avoidedbecause this could cause a temperature run-away or excessive metalsagglomeration. Preferably, the oxygen-containing gas is passed over thebed of catalyst at an initial temperature of about 700°F. to 850°F. toproduce a flame front or combustion zone that travels through thecatalyst bed. The amount of oxygen in the inert gas is controlled toprevent this flame front from exceeding about 950°F. and is preferablymaintained at about 700°F. to 850°F.

After coke burn-off, the catalyst can be activated by treating it atelevated temperature with a halogen-containing gas. In the activationstep, the catalyst, after it has been regenerated, is contacted andreacted with a halogen-containing gas at a temperature from about 500°F.to about 1000°F. Halogen lost during reforming is restored in this step,and redispersion of the metal component, or components, of the catalystis effected.

Following regeneration or activation, or both, of the catalyst, thesystem is purged with nitrogen or other inert gas to remove any oxygenpresent and then the catalyst is reduced with a hydrogen-containing gas.Thereafter, the catalyst is put on-oil, i.e., naphtha and hydrogen arecontacted with the catalyst under reforming conditions.

During an on-oil portion of an operating cycle, reforming is conductedat temperatures ranging from about 600 to about 1050°F., and preferablyat temperatures ranging from about 850° to about 1000°F. Pressures rangegenerally from about 50 to about 750 psig., and preferably from about100 to about 250 psig. The reactions are conducted in the presence ofhydrogen to suppress side reactions normally leading to the formation ofunsaturated carbonaceous residues, or coke, which causes deactivation ofthe catalyst. The hydrogen rate, once-through or recycle, is generallywithin the range of from about 1000 to about 10,000 SCF/Bbl., andpreferably within the range of from about 2000 to about 5000 SCF/Bbl.The feed stream, in admixture with hydrogen, is passed over the catalystat space velocities ranging from about 0.1 to about 25 W/W/Hr., andpreferably from about 1.0 to about 5.0 W/W/Hr.

The invention will be more fully understood by reference to thefollowing selected non-limiting examples and comparative data whichillustrate its more salient features. All parts are given in terms ofweight except as otherwise specified.

In preparing for these demonstrations as described by reference to theexamples below, a platinum-iridium catalyst is prepared by slurrying 1part of particulate alumina, 24 to 35 mesh average particle size(Tyler), in 4 parts of water. Dilute aqueous solutions containingiridium (as chloroiridic acid), and platinum (as chloroplatinic acid),are added and the resultant solution stirred for one hour to assureimpregnation of the alumina. The solids are then separated from thesolution by filtration and dried in a circulating air oven at about220°F; and then calcined in an inert atmosphere of nitrogen for 3 hoursat 1000°F. The platinum-iridium catalyst is then heated to 930°F. in aflowing stream of pure hydrogen. The catalyst, which contains 0.3 weightpercent platinum and 0.3 weight percent iridium, as metallic metal, isthen cooled, in the absence of air, to ambient conditions. Thecrystallite size of metal hydrogenation-dehydrogenation components, asdetermined by X-ray analysis, is well dispersed, showing no agglomeratesas large as 50A, or greater.

The catalyst is then packed as a fixed bed in one of severalhydroforming reactors and contacted with a typical naphtha having thefollowing inspections:ASTM Distillation Initial 224 10 232 20 234 30 23840 241 50 244 60 249 70 253 80 262 90 277 Final B.P. 347Octane No., RONClear 55Gravity, °API 57.4Sulfur, Wt. PPM 0.1Analysis, Vol. PercentParaffins 43 Naphthenes 49 Aromatics 8

The hydroforming reactor is operated at the following on-oil conditionsto produce a C₅ ⁻ liquid gasoline product of 102 RON clear which, fromthe beginning of the run to the end of the run, lasts for approximately6 months.

    ______________________________________                                        Major Process Conditions                                                             Temperature, °F. (Average)                                                              900°F.                                                Pressure, Psig   225                                                          Space Velocity, W/Hr./W                                                                        2.0                                                          Hydrogen Rate, SCF/Bbl.                                                                        5000                                                  ______________________________________                                    

At the end of a run, the flow of feed to the unit is discontinued andthe reactor containing the bed of platinum-iridium catalyst is purgedwith nitrogen to remove residual hydrocarbons. The reaction coke,amounting to about 1-2 weight percent based on the total catalyst, isburned from the catalyst in situ by injecting initially about 0.3 volumepercent oxygen in nitrogen into the reactor while maintaining an 810°F.flame front temperature, and then over a period of 24-36 hoursincreasing the oxygen concentration on the gas to 1.0 volume percentoxygen and continuing the burn at a temperature of 750°F. for a totaltime of 4-6 hours, after which time the catalyst, which contains aresidual of about 0.10 weight percent coke, is found by X-ray analysisto be about 30 percent agglomerated, i.e., 30 percent of the iridium ispresent as agglomerates (containing both iridium and iridium oxide) ofgreater than 50A particle size diameter.

One portion of the agglomerated platinum-iridium catalyst is thenimpregnated with a sufficient amount of an iron salt to provide acatalyst containing 0.3 weight percent platinum, 0.3 weight percentiridium and the desired amount of iron, e.g., 0.5 weight percent iron,as metallic metal, the preparation being conducted as follows: 250weight parts of the agglomerated platinum-iridium catalyst isimpregnated with, e.g., 9.3 weight parts of ferric nitrate, Fe(NO₃)₃.9H₂O, the iron salt being dissolved with stirring, for one-half hour, indeionized water to which 2 weight parts oxalic acid is added. Sufficientadditional deionized water is added to dilute the solution and toimpregnate the catalyst by incipient wetness. The catalyst is then driedin a circulating air oven at 265°F. for four hours. It is then slowlyheated to 1000°F. in a nitrogen atmosphere and calcined at 1000°F. forthree additional hours. The catalyst is then cooled to ambientconditions.

A second portion of the agglomerated platinum-iridium catalyst isimpregnated with the desired amount of bismuth to form a 0.3 weightpercent platinum, 0.3 weight percent iridium and, e.g., 0.66 weightpercent bismuth catalyst, as follows: 175 weight parts of theagglomerated platinum-iridium catalyst is added to 135 weight parts of adilute nitric acid solution containing 2.5 weight parts of bismuth atincipient wetness. The bismuth impregnated platinum-iridium catalyst isdried overnight at 265°F., and then calcined for two hours at 1000°F.under nitrogen.

In each of the several runs described in the examples below, an Inconelreactor is charged with three separate fixed beds of the above-describedcatalysts, the entry and exit beds being charged for control purposeswith a partially agglomerated platinum-iridium catalyst (0.3% Pt/0.3%Ir) while the middle bed, the bed used for the present demonstrations,is charged with a platinum-iridium catalyst, and a platinum-iridiumcatalyst additionally containing iron or bismuth, in specificconcentration hereafter defined.

The examples following show the effectiveness of iron and bismuth, addedto the platinum-iridium catalyst, in promoting redispersion of iridiumagglomerates, when dispersion is effected, by an initial prereductionwith hydrogen, and by contact of the agglomerated catalyst, in a singlecycle treatment to the point of chlorine breakthrough, with a moistchlorine-oxygen containing nitrogen gas at 930°F., and at a pressure of100 psig. The responsiveness to redispersion of an agglomeratedplatinum-iridium catalyst to such treatment is thus compared to theresponsiveness of similarly agglomerated catalysts which contain iron,or bismuth, in addition to platinum and iridium, the agglomeratedcomposition, in terms of the percent iridium and iridium oxide, beinggiven at the entry, mid-portion and exit sides of the middle bed of thereactor at the time of chlorine breakthrough. Percent agglomeration ismeasured by X-ray analysis.

EXAMPLE 1

A platinum, iridium-on-alumina catalyst (0.3 Wt. % Pt, 0.3% Ir),containing 30 percent of the iridium as agglomerates of iridium oxidegreater than 50A (X-ray), is treated with a hydrogen gas mixture, andsubsequently with a moist chlorine gas mixture. Thus, the catalyst isfirst treated with a gaseous mixture of 100 percent hydrogen saturatedwith water for 48 hours at 930°F. The hydrogen is then purged from thebeds with nitrogen. The beds of reduced catalysts are then treated tothe point of chlorine breakthrough with a gaseous mixture of 0.13percent chlorine and 0.13 percent oxygen in nitrogen at 930°F. Aplatinum, iridium, iron-on-alumina catalyst (0.3 Wt. % Pt, 0.3 Wt. %iridium, 0.5 Wt. % iron). 30 percent agglomerated is similarly treated.The results are given in Table I, below:

                                      TABLE I                                     __________________________________________________________________________    Treat Conditions:                                                                            5000 ppm water                                                                0.13% Cl.sub.2 /0.13% O.sub.2 in N.sub.2                                      930°F.                                                                 100 psig                                                                 Percent Agglomeration                                                         (Iridium Metal plus Iridium Oxide)                                            Starting      Middle Exit Side                                                Material                                                                             Entry  of Bed of Bed                                         Catalyst  Ir + IrO.sub.2                                                                       Ir IrO.sub.2                                                                         Ir IrO.sub.2                                                                         Ir IrO.sub.2                                   __________________________________________________________________________    0.3% Pt, 0.3% Ir                                                                        30     19 21  27 17  16 24                                          0.3% Pt, 0.3% Ir,                                                                       30     17  0  11  0  -- --                                          0.5% Fe                                                                       __________________________________________________________________________

EXAMPLE 2

The foregoing example is repeated, except that the H₂ treat lasted 24hours instead of 48 hours, and bismuth is used rather than iron as apromoter for the platinum-iridium catalyst, with the following results:

                                      TABLE II                                    __________________________________________________________________________    Treat Conditions:                                                                            5000 ppm water                                                                0.13% Cl.sub.2 /0.13% O.sub.2 in N.sub.2                                      930°F.                                                                 100 psig                                                                 Percent Agglomeration                                                         (Iridium Metal plus Iridium Oxide)                                            Starting      Middle Exit Side                                                Material                                                                             Entry  of Bed of Bed                                         Catalyst  Ir + IrO.sub.2                                                                       Ir IrO.sub.2                                                                         Ir IrO.sub.2                                                                         Ir IrO.sub.2                                   __________________________________________________________________________    0.3% Pt, 0.3% Ir                                                                        30     19 21  27 17  16 24                                          0.3% Pt, 0.3% Ir,                                                                       30     18  9  21  0  25  0                                          0.5% Bi                                                                       __________________________________________________________________________

EXAMPLE 3

This example shows that a platinum-iridium on alumina catalyst whichcontains iron is more active than a catalyst otherwise similar exceptthat it does not contain iron. Platinum-iridium andplatinum-iridium-iron catalysts are thus used to reform a typical virginnaphtha of boiling range 240°-380°F. containing 20 volume percentaromatics, 40 volume percent paraffins and 40 volume percent naphthenesat 900°F., 3 W/W/Hr., and at 150 psig, to provide a gasoline product of102 RON clear with the following results:

                     C.sub.5 .sup.+ Liquid                                                                     Relative                                         Catalyst Composition                                                                           Selectivity Activity                                         ______________________________________                                        0.3% Pt/0.3% Ir/0.7% Fe                                                                        79.0 LVS    565                                              0.3% Pt/0.3% Ir  79.0 LVS    305                                              ______________________________________                                    

This demonstration presents comparisons between a platinum-iridiumcatalyst and platinum-iron catalysts, the runs being conducted at925°F., 1.1 W/W/Hr., and 200 psig using a virgin naphtha of boilingrange 210°-350°F., which contains 12 volume percent aromatics, 62 volumepercent paraffins and 26 volume percent naphthenes. The runs are carriedout under identical conditions with differences in catalyst activitydetermined by differences in percent aromatics in the product (relatedto RON), as follows:

                   Wt. %                                                                         Aromatics    Relative                                          Catalyst       in C.sub.5.sup.+                                                                           Activity                                          ______________________________________                                        0.3% Pt/0.3% Ir                                                                              75.5         305                                               0.3% Pt/0.1% Fe                                                                              59.4         83                                                0.3% Pt/1.0% Fe                                                                              51.0         55                                                ______________________________________                                    

Having described the invention, what is claimed is:
 1. A catalyst fordehydrogenation and dehydrocyclization of paraffinic naphthas comprisinga composite including a porous inorganic oxide support, halogen inconcentration ranging from about 0.1 to about 2 percent, platinum inconcentration ranging from about 0.05 to about 3 percent, iridium inconcentration ranging from about 0.05 to about 3 percent, and iron orbismuth in concentration ranging from about 0.5 to about 5 percent,based on the total weight of the catalyst.
 2. The catalyst of claim 1wherein the catalyst composite contains from about 0.6 to about 1.5percent halogen, from about 0.1 to about 0.6 percent platinum, fromabout 0.15 to about 0.3 percent iridium, and from about 0.5 to about 2percent iron or bismuth.
 3. The catalyst of claim 1 wherein the halogenis chlorine.
 4. The catalyst of claim 1 wherein the porous inorganicoxide support is alumina.
 5. The catalyst of claim 2 wherein the halogenis chlorine.